1. Field of the Invention
The present invention is in the field of mold inhibiting products and methods, and also relates to the prevention of harmful dust which is likely to be generated in the handling and use of some products which also characteristically have mold problems, such as grains, animal feeds, animal feed ingredients, and hay.
2. Description of the Prior Art
a. Mold Problems
There is a serious worldwide problem of molds growing in food materials, and particularly in grains, animal feeds, animal feed ingredients, and hay. This problem is most serious, and is a year-round problem, in tropical zones of both the eastern and western hemispheres, where sustained high humidities cause excessive moisture to be absorbed in such products, particularly during storage, but also in transit.
This mold problem is also serious in temperate and colder zones on a short-term basis where there are frequent large temperature differentials between night and day, on the order of about 20.degree. F. or more, as occurs in many temperate locations, particularly during the spring and fall seasons; and also on a long-term basis where there are large temperature differentials between the fall harvesting season in which grains are stored and the following winter season during which the storage continues or during other extended periods of storage.
One reason molds present such a serious problem is that they produce dangerous mycotoxins, some of which are carcinogenic. For example, one of the common molds, Aspergillus Flavus, produces the mycotoxin aflatoxin which, in addition to other toxic characteristics, interferes with the immune system's ability to produce gamma globulin, the protein that is part of the immune system. The resulting breakdown of the immune system then renders animals that have ingested such mold vulnerable to a variety of diseases.
Mold spores are ubiquitous in the air throughout most of the world, but a primary factor in their ability to propagate on any product is the moisture content of that product. It is well-known in the art that if the moisture content of any product such as grains or feeds is less than approximately 13.5 percent by weight, then the ability of molds to propagate is so seriously limited that mold damage is of little or no concern. However, as the moisture level in the product increases above about 13.5 percent, the vulnerability of the product to mold propagation increases at a surprisingly rapid rate. For example, for applicant's propionate ion-containing mold inhibiting compositions defined in the aforesaid "Related Applications," applicant prescribes the use of three to five pounds per ton of his products for 14 to 16 percent moisture content by weight, 4 to 6 pounds of his product for 16 to 18 percent moisture content by weight, and 5 to 7 pounds of his product for 18 to 20 percent moisture content by weight. Thus, for only about a 4 percent average increase in moisture content, more than a 30 percent increase in the mold inhibiting product is considered by applicant to be desirable for the control of mold propagation.
In view of such sensitivity of molds to the moisture content of products like feeds and grains, the primary means for controlling mold propagation in the art has historically been to limit the moisture content of the products, preferably to not more than approximately 13.5 percent by weight of moisture. Probably the best example of such moisture limitation is the conventional practice for many years of drying grains down to below approximately 13 to 14 percent moisture content by weight in preparation for storage in grain elevators or silos.
However, despite the effectiveness against mold propagation of the procedure of limiting the percentage by weight of moisture in grains or feeds, there are still serious problems to be overcome. For example, where grains are dried down to below approximately 13 to 14 percent moisture content by weight for storage, the feeding quality and efficiency of the grain is impaired when it is so dry, so that it is conventional practice in some areas to add back moisture to the grain after it has been removed from storage to improve its feeding quality and efficiency for cattle. Nevertheless, the feeding quality and efficiency of the grain still remains somewhat diminished by the grain having been subjected to the sucessive steps of drying and remoistening. These steps of drying and remoistening the grain are also disadvantageous because they add materially to the cost of the product.
The most serious problem, whether or not grain, feed or feed ingredients have a moisture content of below about 13 to 14 percent by weight, is that in any bulk storage or transport of grain, feed, or feed ingredients, whether it be grain elevators, silos, tanks, feed bins, railroad tank cars, trucks, barges, ships, or the like, where there develops a substantial temperature differential between relatively warm central regions of the bulk and relatively cold peripheral regions of the bulk, moisture will migrate from the relatively warm central region to the relatively cold peripheral regions, accumulating in the peripheral regions to increase the moisture concentration there, and consequently increase the vulnerability of the products to mold in the peripheral regions. This is true on a short-term basis where the products are stored or transported in tanks, bins, barges or ships at locations where there are large overnight temperature drops, on the order of about 20.degree.-40.degree. F., even with products that have a low moisture content. It is also true on a long-term basis where grains are stored in elevators or silos, being harvested and stored during the fall when temperatures are moderate, and retained in the storage facility through the cold winter months, and sometimes for years. Here, the seasonal temperature differential between inner and outer portions of the grain bulk may be very large, particularly in inland regions such as the plains states of the United States and western Canada.
Referring to the short-term moisture migration problem which occurs in tanks, bins or other containers for grain, feed or feed ingredients where there are large overnight temperature drops, such temperature drops will lower the temperature of the container walls, establishing a large temperature differential between the walls of the container and the temperature of the material within the central region of the container. Water molecules have the characteristic of moving from a warmer zone toward a colder zone, and thus will move or migrate from the central region of the container through the bulk of the material toward the cold walls of the container, increasing the humidity and dampening the material near the walls to provide an excellent growing medium for molds in that region; and this is recognized as a major problem when the humidity level increases to the point where moisture actually condenses on the walls of the container. In many cases, the condensed moisture will drip into the product from the top of the container, and in addition to making it more conducive for mold growth, also serves to deteriorate the quality of the product in other ways. After a few repeated nights of a temperature differential on the order of about 20.degree.-40.degree. F., mold spores which are present all of the time will become active and propagate.
Even with grain, feed or feed ingredients having an average moisture content of 13.5 percent or less, which is conventionally considered to be safe from any substantial mold problem, the moisture content in the material adjacent the container walls will be cumulatively raised higher and higher night after night of such temperature differentials, and a substantial mold problem will develop.
While this may appear to be a localized problem affecting grain, feed or feed ingredients only adjacent container walls, it is likely to grow into a much more extensive problem in the bulk of stored material. It is recognized in the art that even small damp patches of grain or feed in a stored bulk will be likely to initiate development of mold and other adverse growths throughout the bulk of the feed or grain.
This same water migration problem toward cold container walls occurs in connection with the shipping of compressed hay cubes. In the overseas transportation of hay, it is common practice to compress the hay into cubes, and ship such compressed hay cubes in large batches in steel containers. For example, one company of which applicant is aware ships compressed hay cubes in large steel containers. The hay is required to be relatively moist to be compressed into cubes, as for example having a moisture content of approximately 15-16 percent by weight. While such moisture content is not likely to cause a substantial mold problem during the typical 2-3 week voyage if the moisture were to remain substantially uniformly spread throughout the compressed hay, large day/night temperature differentials are frequently encountered during ocean voyages, and in such case, moisture migrates from relatively warm central portions of the containers toward and onto the walls of the containers, greatly increasing the percentage of moisture in the hay adjacent the walls, causing the hay to get moldy in such regions.
The first recognition in the literature of this short-term moisture migration problem in grain of which applicant is aware was a 1969 article by R. W. Disney entitled "The Formation of Dew on a Cooled Surface in Contact With Wheat" (J. stored Prod. Res., 1969, Vol. 5, pp. 281-288. Pergamon Press. Printed in Great Britain). This publication describes a series of tests run by Disney proving the migration of moisture from a warm region in a body of wheat to a relatively cold container wall. Disney theorized in the article that the grain is initially in equilibrium with the intergranular atmosphere but as the container surface is cooled, the relative humidity of the adjacent atmosphere rises and the temperature of the nearby kernels falls, upsetting the equilibrium and causing the kernels near the container surface to absorb water from the air.
Facilities such as grain elevators or silos for the long-term storage of grains which are subject to a large seasonal temperature differential between the fall season when grains are stored and the following winter through which storage continues will have the same moisture migration, or translocation problem, as described in detail above for short-term moisture migration in tanks, bins, or the like. The resulting mold problem in long-term storage facilities can be at least as severe, and sometimes even more severe, than in short-term metal storage containers, because of the extended period of time during which grain may be subjected to generally saturated moisture conditions in zones adjacent walls of the storage facility over the extended storage time and also because of the very large quantities of grain often stored in such facilities. This problem is even more severe where grains are stored for successive years.
Applicant is aware of two early publications which rcognize this long-term moisture migration problem, but which do not offer any practical solution. The first of these publications was by Anderson et al. in 1943, entitled "The Effect of Temperature Differential on the Moisture Content of Stored Wheat" (Canadian Journal of Research, Vol. 21, sec. C, pp. 297-306). This publication reports on grain elevator annexes in western Canada each of which held about 30,000 bushels in one pile, the annexes being filled in the fall with sound high-grade wheat of low moisture content, with no ventilation provided above the wheat. In the spring a layer of damp grain 1-2 feet deep had been found to have developed at or near the surface of the grain in a number of the annexes, with moisture contents of 16-18 percent not uncommon. The only cure employed was removal of the damaged grain and fumigation of the remainder when the latter seemed advisable. Prevention methods were crude, including some means of ventilation that could be closed during rain and snow storms, and if the moisture content started to increase near the surface, the grain was shoveled over and thus dried. Long-term experiments were performed on wheat which had a uniform starting moisture content of 14.6 percent. At the end of 316 days, the driest sample taken from the warm zone of the bulk of wheat had a moisture content of 10.9 percent, and the wettest sample taken from the cold zone of the bulk had a moisture content of 29.6 percent.
The second publication of which applicant is aware relating to long-term moisture migration or translocation in bulk stored grain was by T. A. Oxley entitled "The Movement of Heat and Water in Stored Grain" [Am. Ass. Cer. Chem., Transactions 6:84-100 (1948)]. From the last paragraph on page 96 to the top of page 98, Oxley provides an excellent scientific discussion of the mechanism whereby whenever a mass of grain has parts at different temperatures, there is a movement of water from hotter to cooler parts. At page 95, second full paragraph, Oxley indicates the danger of even small damp patches of grain in a bulk of grain, such patches being likely to initiate heating, insect development, and perhaps fungal growth which will spread throughout the bulk; stating that in practice the life of a bulk of grain often is determined by its dampest parts. At page 95, last paragraph, Oxley states that according to frequent observations, some "pockets" of damp grain will certainly persist in otherwise dry bulks for months and even years, and states the common remedy of mixing "tough" with dry grain in order to dry the former which, of course, is a very crude and inconvenient sort of remedy.
A further publication entitled "Diffusion of Moisture Through Grain" by Pixton and Griffiths (J. stored Prod. Res., 1971, Vol. 7, pp. 133-152. Pergamon Press, printed in Great Britain), at page 135 stresses the importance of temperature gradient moisture translocation in grain, as follows: "Translocation of moisture due to temperature gradients is responsible for the mold, caking, sprouting and rotting which occur at the surface of a warm bulk of grain. By itself heating may not damage the grain, but the secondary effects caused by moisture translocation are the main cause of serious damage (Oxley, 1948a). The importance of moisture behavior in the storage, transport and handling of grain cannot be over emphasized. It is one of the most important items in grain technology, the moisture content mainly determining whether the grain will store free from deterioration or not."
b. Dust Problems
In addition to the foregoing mold problems, there are also serious dust problems in connection with the use, handling, and storage of some of these same materials for which there are mold problems as described above.
Dust from animal feeds or feed ingredients is a widespread problem, with a potential for causing lung diseases in various animals, such as horses, cattle, hogs, sheep, and poultry. By way of example, one such dust problem of which applicant is aware that occurs in connection with animal feeds relates to poultry feed. The tips of poultry feed granules have a tendency to dry out and break off from the feed granules, and turn into dust. Such dust when breathed in by the birds can cause serious respiratory diseases such as Aspergillosis.
This same problem occurs with respect to the poultry litter. The litter tends to dry out and generate dust which, when breathed in by the birds, can cause the same diseases as feed dust.
Dust has historically been a serious problem in connection with the storage of grains, as in grain elevators. Dust is generated by screw conveyors conventionally employed to convey grain into elevators, dry surface portions of the grain particles being ground off into dust. This can result in a catastrophic explosive atmosphere in a grain elevator where too much dust is generated and dispersed through the air in the elevator. This problem is compounded where the grain is dried prior to storage down to below 13-14 percent by weight moisture as a mold-inhibiting measure.
c. Bridging and Caking Problems
Another problem in the handling of grain and animal feed is that it tends to cake and "bridge." Moisture from inside the body of grain or feed appears to migrate to a location proximate the walls of the storage bins, including the bin gates. Also, respiration appears to occur in the grain or feed from poor air circulation resulting from such moisture, causing a spontaneous heating and generation of further moisture as a byproduct of the respiration. Accumulation of such moisture causes the caking and bridging to occur, and this produces agglomerations of grain or feed which do not flow freely, and blocks the flow of grain or feed when the gate is opened. This is such a widespread problem that a rubber mallet is placed next to most feed bins in the United States so that the caking and bridging can be shattered by striking the wall of the bin to start the grain or feed flowing.